In order to pump oil from a well in which casing has been set, the casing is perforated by a suitable gun at those levels at which oil has been indicated to exist. After the casing has been perforated, a pump is lowered on the end of the conventional drill pipe string to this particular level. The pump includes a pumping tube hereafter referred to as a pump barrel within which a reciprocating plunger operates. This plunger is driven by sucker rods extending upwardly through the pipe string to the surface of the well. Oil is pumped from the lower well annulus adjacent to the perforations in the casing up through the well tubing or pipe string to the surface of the well.
After pumping has been completed, or if it is desired to change the pump or repair it, it is necessary to pull the pipe string or tubing to bring the pump to the surface. Since, however, the oil well pipe string is filled with oil throughout the length of the tubing, whereas the surrounding oil in the well annulus defined between the exterior of the pipe string and interior of the casing is at a relatively low level, there exists a very large pressure differential rendering it extremely difficult to unseat the pump to remove the same or to pull the pipe string.
The foregoing condition can be overcome if the fluid or oil within the pipe string could be passed in a reverse direction to the annulus exterior of the pipe string. If the fluid could be passed in this manner, the large hydrostatic head created within the well tubing string could be "dumped" into the surrounding annulus of the well and thus equalize the pressure involved so that removal of the tubing or well string without the large hydrostatic head of oil could be readily achieved.
My U.S. Pat. Nos. 3,168,873 issued Feb. 9, 1965; 4,047,853 issued Sept. 13, 1977 and 4,157,117 issued June 5, 1979 all relate to hydraulic unloading devices which solve the foregoing problem. However, the solutions described in these patents all involve special components, ports, and the like not normally provided in the conventional pipe string for providing the reversed flow path when "dumping" is to take place. These ports can become clogged by sand and thus rendered ineffective. In addition, while my latest patent is adaptable to a special type of pump known as the "HOPS" pump, my earlier patents do not describe systems which could be used on such a pump.
It would be advantageous if an appropriate hydraulic unloading system or bypass valve assembly could be provided which is not subject to clogging by sand and which is adaptable to all types of oil well pipe strings incorporating a pump operated by sucker rods.